In the last 20 years roundabouts have become very popular in The Netherlands.
After the right of way rules changed, roundabouts became an effective alternative
to the traditional four arm junction.
The modern Dutch roundabouts have a good capacity
and they have proven to be a lot safer than traditional junctions.
Not only for motor traffic, but also for walking and cycling.
So what features make that possible?
First of all that is the relatively small circle and the fact that the entrances
are at a rather sharp angle.
This forces motor traffic to enter the roundabout at a low speed,
around 25 to 30km per hour.
Due to the tight radius of the circle and that of the exit as well,
motor traffic cannot accelerate until after it has left the roundabout altogether.
So the speeds stay low on the entire passage.
Exactly where the speeds are lowest at the entry and exit points
is where the crossings for walking and cycling are located.
Unlike traditional intersections that need a lot of lanes for each direction,
for traffic to wait for the lights to change,
most roundabouts only need a single access lane.
This gives an uncluttered and easily understood street design, that uses a lot less space.
It also makes the crossing distances for walking and cycling a lot shorter and thus safer.
If necessary there can be a central refuge island to break up the crossing.
This will shorten it even further.
It also gives people walking and cycling the opportunity to deal with traffic from one direction only.
Only after they have passed the central refuge island, they have to deal with traffic
coming from the opposite direction.
In the built up area Dutch design manuals recommend to give cycling priority
over motor traffic on the roundabouts.
If that is the case, walking should also have priority.
This can be achieved with zebra crossings.
To make that priority arrangement instantly clear to all road users,
the red asphalt of the circular cycleways will continue all the way around the roundabout.
Apart from the standard yield signs and the so-called sharks teeth,
that are a further indication of the priority arrangement.
To decrease motor speeds even further, the crossings can be built on a raised table.
It is best to have the crossings for walking and cycling at a distance of about
6 metres from the ring for motor traffic.
That gives the driver of a motor vehicle the space to yield and wait
in between that ring and the crossings
without being in the way of other traffic
In the countryside, outside the built up area,
it is recommended that people cycling and walking should yield to motor traffic.
To make that clear the cycleways shouldnt be as circular
and the red asphalt should be interrupted.
But here too, there will be yield signs
and the so-called sharks teeth on the surface to indicate that.
Such crossings should also be a bit further away
from the motor traffic circle.
Preferably about 10 meters, so in effect they become separate crossings
with almost no relation to the roundabout.
For roundabouts that have to handle higher volumes of motor traffic,
it can be necessary to build more than one traffic lane.
The big disadvantage of more than one lane is that motor vehicles can mask other vehicles,
which makes level crossings for walking and cycling more dangerous.
And even more so because the bigger radius of multi-lane roundabouts
leads to higher speeds of motor traffic.
A further disadvantage is the tendency for car drivers to change lanes on the roundabout itself.
Leading to unexpected, dangerous behaviour.
A design improvement for multi-lane roundabouts
is a Dutch innovation called the Turbo roundabout.
On a Turbo roundabout it is not possible to change lanes on the roundabout itself.
Usually there are actual ridges between the lanes to physically prevent a lane-change.
Drivers chose their lane for their direction ahead of the roundabout,
and are unable to deviate from their chosen path
until after they have left the roundabout.
This leads to a predictable behaviour and a high traffic throughput
at relatively low speeds.
The turbo-roundabout doesnt eliminate the danger of the level crossings.
If there is no other option such a crossing should be at a considerable distance.
But most often turbo roundabouts are combined with overpasses
or underpasses for walking and cycling.
The safety, the easily understood design, the space efficiency
and the capacity of modern Dutch roundabouts
makes them very popular with road managers.
but also with road users.
Even the more vulnerable road users, people walking and cycling
prefer roundabouts over signalised intersections.
The fast traffic flow and the safe and logical design
makes roundabouts very convenient.